Various types of blood coagulators have been developed in the art to clot the blood, which minimizes the danger resulting from excessive loss of blood during surgical operation. In particular, plasma coagulators which transform inlet gas to plasma and clot the blood by applying the plasma to the tissue during surgical operation, have been widely used in clinical surgery and actively studied by researchers, due to its simple structure and high coagulation efficiency.
For example, U.S. Pat. No. 3,903,891, U.S. Pat. No. 3,938,525, U.S. Pat. No. 3,991,764, U.S. Pat. No. 4,562,838, U.S. Pat. No. 4,781,175 and U.S. Pat. No. 5,207,675 disclose various types of plasma coagulators known in the art.
The plasma coagulators of the prior art are generally classified into two classes, in accordance with their structure, and principle or mode of plasma generation:
One type of plasma coagulators comprise a power supply, gas dynamic path and plasmotron. A cylindrical case of the plasmotron has an output channel for plasma, an anode connected to an electrical circuit of a power supply, and a cathode connected to a cylindrical holder installed coaxially with the case and a rod-like electrode fixed in the end of the holder. The plasma is generated from the plasma forming chamber located between a free end of the electrode and an internal sectional face of the output channel in the form of an arc or glow discharge generated between the anode and the cathode.
The plasma coagulators of the prior art, however, have revealed shortcomings as follows: they essentially require a large cooler and a heat exchanger to cool a heated head of the plasmotron, because the plasma is formed during heating to over several thousand degree of temperature, and the arc generated between the electrodes is very unstable. Further, when the plasma coagulator is practically operated, shunting of the arc arises and the laminar flow of plasma may be disturbed, which finally produces an unstable plasma. When the charge of plasma forming gas is low, unstable plasma is also generated and the plasma discharge can be stabilized only by regulating the charge of gas, which results in malfunction of the plasma coagulator. The limitations of the prior art are presumed to be caused be the fact that the length of the plasma arc is fixed by a variety of parameters dependent on power supply and gas dynamic path, e.g., arc current, charge and pressure of gas, and the diameter of the output channel in the plasma coagulator.
Moreover, the plasma coagulators of the prior art have low coagulation efficiency and increased weight and dimension, and they essentially require an extra ballast resistance in order to regulate the parameters of the power supply and load, and to compensate for the lowering of Volt-Ampere characteristics of the plasma coagulator.
Another type of plasma coagulator comprises a high frequency power supply, gas dynamic path and plasmotron. The plasmotron is assembled in a cylindrical case where a high frequency inductor is positioned, and a dielectric tube functioning as a chamber for plasma generation is located on the axis of coil to help provide the outlet of plasma forming gas. In the plasma coagulator of this type, voltage generated from the high frequency generator which operates at a frequency of tens of MHZ, is transferred to the inductor, and gas flow in the dielectric tube is heated up by the conductive ring current flow, which finally generates the plasma.
The plasma coagulators of the prior art of this type, however, have the disadvantages as follows: the plasma generated from the plasma coagulator are of very high temperature of 4,000 to 9,000.degree. C. and a high frequency current directly conducting to the tissue may be generated from the plasma coagulator, which possibly causes fatal damage to the tissue during surgical operation, and takes a long time to coagulate the blood.
Further, the prior art plasma coagulators, in general, have low coagulation efficiency and it is essential to heat the coil to a high temperature by employing a large capacitor; and, therefore, the mass and dimension of power supply naturally increases to provide the high electric conductivity during gas flow. Especially, when the plasma coagulators of the prior art are applied to the tissue which bleeds in high volume, e.g., to the liver, it is known that the prior art coagulators have very low coagulation efficiency. Moreover, the energy consumption of the coagulators is more than thousands of kV, and an electric shock may be caused when the coagulators are practically used, because the plasma generated therefrom has bipolar characteristics. The prior art plasma coagulators, also, have very complicated structure, which results in increase of the costs for manufacturing. Accordingly, they have been proven to be less satisfactory in the sense that they can not be practically used in clinical surgery.